There appears to be a critical percentage of body fat necessay for the onset of the menses. This project will examine maturation of reproductive function in a population of adolescent females with a reduced body fat content due to athletic training. Skinfold thicknesses at the triceps and iliac sites, height, weight, and body density measurements will be taken in samples of female swimmers ages 8 to 17. Questionnaire data from each girl will determine the age of menarche cycle regularity or irregularity, other menstrual disorders, and general health history. In addition, identical data will be obtained from a cohort of girls of similar age who are not involved in intensive athletic training. Regression equations for determining percentage body fat using the triceps and iliac skinfold thicknesses and underwater weight will be developed for the athletic and non-athletic groups. The effect of athletic training of 12 months and 5-6 months duration upon reproductive devlopment and stature will be examined. The effect on the relative height for age will be examined by performing a cross-sectional analysis of height data. It is hoped that this study will further clarify the relationship between body fat content and ovarian function and lead to more comprehensive studies of the effects of intensive physical training upon pre-adolescent and adolescent female growth, specifically the relationship to the onset of menstruation, and the energy storage requirement of pregnancy.